Acrylic compositions and articles made from them are well known for their clarity, sparkling color, and surface gloss. Acrylic materials also tend to have low impact strength or brittleness, and have marginal chemical resistance to medical/bio-pharmaceutical agents.
Plastic materials have found use in medical and biopharmaceutical applications. These applications require transparency, a high level of impact resistance, as well as chemical resistance to lipids and solvents—in particular isopropyl alcohol. The chemical resistance is generally tested with the material under strain. The plastics must also flow well at normal processing temperatures, to form articles. The plastic articles may be reusable (sterilizable) or single use articles.
Copolymers of acrylics with styrene have been used in medical and biopharmaceutical applications. The styrene allows for material that can easily flow during processing, as well as contributing to the chemical resistance.
U.S. Pat. No. 5,2219,931 describes blends of polyvinylidene fluoride (preferably 4-50 wt. %) with core-shell acrylic copolymers (preferably 50-96 wt %) to produce solvent-resistant thermoplastically processible polymer mixtures. The reference describes acrylic polymers that are highly crosslinked, and not uncrosslinked methyl methacrylic polymers.
U.S. Pat. No. 6,689,827 describes transparent impact-resistant thermoplastic molding materials in which the matrix polymer is a blend of a methylmethacrylate/acrylate and styrene/acrylonitrile copolymers.
WO 2007/064529 describes capstock compositions containing low levels of polyvinylidene fluoride. The reference fails to recognize the need for flow-aids when processing high molecular weight acrylic compositions.
Polyvinylidene fluoride polymers have been used to modify acrylic polymers, as described in U.S. Pat. No. 4,868,036 having from 10 to 45 weight percent of polyvinylidene fluoride polymer; and in US 2007/0185270 having 30-95% by weight of fluoropolymer.
U.S. Pat. No. 5,599,863 describes the use of selected polyalkylene glycols in addition to butylated hydroxyl toluene to improve the gamma radiation sterilization of acrylic polymers.
There is a need for an all-acrylic thermoplastic material, having no styrene or other comonomers, that can meet the performance standards in today's medical and biopharmaceutical applications. The main criteria are a high solvent resistance (isopropyl alcohol) and lipid resistance. The lipid resistance includes resistance to the more aggressive lipids often found in home-use applications, i.e.—for cancer drugs. The composition must also have good process flow properties, to form intricate parts. For example, the newest generation of oncology (cancer) drugs uses lipids as a carrier to introduce the drug into the body. The most current lipid resistant polycarbonates were upgraded to meet the increasing demand for lipid emulsions to administer non-water soluble pharmaceuticals. But according to medical device manufacturers these PC grades are still deficient in their performance.
Surprisingly, it has been found that a relatively high molecular weight all-acrylic copolymer matrix, blended with a small amount of polyvinylidene fluoride (PVDF) and other additives, can provide the required chemical resistance, clarity, and flow to meet the industry requirements for a transparent plastic material. Prior art does not mention an acrylic copolymer that both improves melt processing behavior while not harming chemical resistance of an impact acrylic formulation. We have developed a transparent impact acrylic alloy medical grade polymer that offers exceptional chemical resistance while retaining the desirable properties of-a non-styrenic based acrylic impact thermoplastic material.